Conformable heated mattress

ABSTRACT

Embodiments include a conformable heated mattress for patient warming during surgery. The mattress may include a base layer coupled to an operating table and a heated layer coupled to the base layer. The heated layer may include an electrical heating element. The heated layer is coupled to an opposing surface of the base layer at a portion of the opposing surface forming an attached area. The attached area is less than an area of the opposing surface allowing at least a portion of the heated layer to be folded substantially independently of the base layer. Embodiments also include a method of positioning a patient on such a heated mattress.

PRIORITY

This application claims priority to U.S. Provisional Application Number 61/812,987, Flexible Electric Heaters, filed on Apr. 17, 2013, the disclosure of which is hereby incorporated by reference in the entirety.

FIELD

This disclosure generally relates to systems and methods for surgical patient warming.

BACKGROUND

Heated mattresses and heated mattress overlays for therapeutic patient warming are generally well known. Therapeutic patient warming may be useful for patients during surgery. It is well known that without therapeutic intra-operative warming, anesthetized surgical patients may become clinically hypothermic during surgery. Hypothermia has been linked to increased wound infections, increased blood loss, increased cardiac morbidity, prolonged ICU time, prolonged hospital stays, increased cost of surgery and increased death rates.

Heated water mattresses for use during surgery have been available for decades. The warm water mattresses are typically relatively stiff and inflexible. The patient may not sink into the mattress, therefore effectively touching the mattress only across their shoulders, buttocks and the back of their legs. The smaller body surface area in contact with the mattress may result in two problems. First, the smaller surface area supports the entire weight of the patient. As a result, the combination of pressure applied to the boney prominences and the heat from the warm water mattress may both reduce blood flow and accelerate metabolism, causing accelerated ischemic pressure injuries to the skin (“bed sores”). Second, the effectiveness of conductive heat transfer is proportional to the surface area in contact with the heat. A smaller area in contact with the heated water mattress can make the mattress ineffective for patient warming during surgery.

Electrically heated pads and blankets for the consumer market have been made with resistive wire heaters. In use, wire-based heaters have questionable safety. In the operating room environment with anesthetized patients, hot spots caused by the wires in normal use and the failure mode of broken heater wires resulting in sparking, arcing and fires may prevent their use in operating rooms.

Sheet-like, flexible electrical resistance heaters have been shown to be more effective in warming the patients because of the even heat production and generally do not cause arcing and sparking when they fail. The sheet-like electric heaters may be made of conductive or semi-conductive cloth, film or ink. An example of these mattresses is disclosed in U.S. patent application Ser. No. 13/422,279, Heated Under-body Warming Systems, which is hereby incorporated by reference in its entirety. The electrically heated mattresses generally have one or more layers of compressible foam with an overlaying heater layer. Additionally, they may have another layer of foam or fibrous material overlaying the heater. Finally the whole mattress may be enclosed in a waterproof shell.

Such electric mattresses are much more compressible and accommodating than the hard vinyl water mattresses. Further, unlike the water mattresses, the electric heaters do not harden or stiffen over time. Because the electrically heated mattresses are more compressible and accommodating, the patients sink into the mattress and thus more body surface area is recruited to help support the weight of the patient. If the proper foam materials are chosen, virtually the entire posterior surface of the patient can contact the mattress. In comparison to the old water mattresses, the added body surface contact area reduces the pressure applied to the pressure points and simultaneously increases the surface area available for heat transfer. However, even with the added contact surface area, these mattresses may be incapable of transferring enough heat to maintain patient normothermia, especially in pediatric patients.

The limitation in heat transfer is related to the fact that even though the entire anterior or posterior surface of the patient may be in contact, the surface geometry of the mattress may prevent mattress contact with the surface areas of the patient's sides. As the patient sinks into the foam mattress, the upper layer of the protective shell material and the heater layer can create an indentation with gradually tapered sides. Steeply tapered sides would be preferable for conductive thermal contact. It may be physically impossible for a foam mattress with a plastic film cover to closely conform to a patient's shape. The foam and overlying heater layer adjacent the side of the patient may taper away from the patient. Thus, even though the patient may have sunken into the foam, only a small additional surface area long their posterior sides may be in thermal contact.

Another concern with foam mattresses involves their use with pediatric patients. The light weight of the pediatric patient (e.g., in comparison to an adult) may prevent them from sinking into the foam mattress. Therefore, forming the foam around the patient's body thereby increasing the contact with their side surfaces may be challenging to achieve in the case of pediatric patients.

Surgical patient warming mattresses with a greater heat transfer capacity are needed.

SUMMARY OF THE INVENTION

Certain embodiments of the invention include a conformable heated mattress for therapeutic under-body warming during surgery. The mattress may include a heated layer with an electrical heating element, and a base layer coupled to the operating table. The electrical heating element may have elastic properties. The heated layer may have a first sheet of a shell, and a second sheet of the shell. The first and second sheets may be bonded together around their peripheries to form a substantially liquid-proof enclosure, wherein the electrical heating element is sandwiched between the first and second sheets. The heated layer can be coupled to an opposing surface of the base layer at a portion of the opposing surface forming an attached area. The attached area may be less than an area of the opposing surface allowing at least a portion of the heated layer to be folded substantially independently of the base layer.

Certain embodiments of the invention include a method of positioning a patient on a heated mattress. The method may include the step of providing a conformable heated mattress according to certain embodiments of the invention. The base layer may then be positioned on an operating table. The patient may be positioned on top of the heated layer. One or more portions of the heated layer may be folded upwards and lateral to the sides of the patient. A positioning roll may then be placed between the heated layer and the base layer to hold the heated layer proximate the sides of the patient.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of particular embodiments of the present invention and therefore do not limit the scope of the invention. The drawings are not necessarily to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description. Embodiments of the invention will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements.

FIG. 1 is a perspective view of a heated mattress according to an embodiment of the invention;

FIG. 2 is a perspective view of the heated mattress of FIG. 1 with the heated layer in a detached position;

FIG. 3 is a perspective view of the base layer of the heated mattress of FIG. 1 according to an embodiment;

FIG. 4 is an exploded cross-sectional front view of the heated mattress of FIG. 1;

FIG. 5 is a top view of the heated mattress of FIG. 1 according to another embodiment with the base layer and the heated layer attached at a first end;

FIG. 6 is a top view of the heated mattress of FIG. 1 according to another embodiment with the base layer and the heated layer attached at a second end;

FIG. 7 a top view of the heated mattress of FIG. 1 according to another embodiment with the base layer and the heated layer attached along the central region of the mattress;

FIG. 8A is a front view of the heated mattress of FIG. 1 with a patient positioned on the midline trough of the mattress;

FIG. 8B is a front view of the heated mattress of FIG. 1 with a patient positioned on the midline trough of the mattress and the heated layer lifted upwards and laterally around the sides of the patient;

FIG. 8C is a front view of the heated mattress of FIG. 1 with a patient positioned on the midline trough of the mattress and a positioning roll placed between the heated layer and the base layer; and

FIG. 8D is a front view of the heated mattress of FIG. 1 with a patient positioned on the midline trough of the mattress and two positioning rolls placed between the heated layer and the base layer.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides some practical illustrations for implementing exemplary embodiments of the present invention. Examples of constructions, materials, dimensions, and manufacturing processes are provided for selected elements, and all other elements employ that which is known to those of ordinary skill in the field of the invention. Those skilled in the art will recognize that many of the noted examples have a variety of suitable alternatives.

Embodiments of the invention include a conformable heated mattress for therapeutic under-body warming during surgery. Such embodiments may also be used in heated blankets and similar body warming systems typically used for medical applications (e.g., in surgery). For instance, certain embodiments of the invention can be incorporated into the heated mattress inventions disclosed in U.S. patent application Ser. No. 13/422,279. Embodiments of the invention described herein may be described in U.S. Pat. No. 7,714,255, Bus Bar Attachments for Flexible Heating Elements, U.S. patent application Ser. No. 13/422,279, Heated Under-body Warming Systems, U.S. Pat. No. 8,283,602, Heating Blanket, the disclosures of each of which is hereby incorporated by reference in its entirety. The heated mattress according to certain embodiments facilitates improving heat transfer between the patient and the mattress by increasing the surface area of contact between the mattress and the patient's body. Certain embodiments may increase the surface area of contact by substantially separating the patient support functions of the mattress from the patient warming functions of the mattress. By separating these two functions, each function, i.e., support for the patient and patient warming, can be simultaneously provided and maximized independently. Such embodiments provide a safe and effective heated support surface for surgery.

As seen in FIGS. 1 and 2, some embodiments of the heated mattress 10 include a base layer 20 that can be attached to the surgical table e.g., via the islets 22. Various embodiments may also have a heated layer 30 that is substantially separate from the base layer 20 (FIGS. 1-3). As best seen in the cross-sectional view of FIG. 4, the base layer 20 may be conformable and may include one or more layers of foam 24. The foam 24 can be polymeric foam that may maintain the planar shape of the base layer 20. The foam 24 may provide pressure relief and planar stiffness. The layer of foam 24 may have a central region that is easily compressible when a weight of the patient acts on it to provide maximal accommodation for light weight patients such as pediatric patients. Surrounding the central region of soft foam may be a frame-like border of stiffer foam that may effectively keep the base layer 20 spread out and planar. The foam provides pressure reduction in supporting the patient, and gives the base layer 20 enough planar stiffness to prevent it from folding or bunching in use.

With continued reference to FIG. 4, the mattress 10 may include a heated layer 30 with an electrical heating element 34. The electrical heating element 34 may receive current supplied via electrical terminals (e.g., bus bars, not shown) and generate heat due to its electrical resistance. The electrical heating element 34 may be a conductive or semi-conductive fabric coupled (e.g., sewn via electrically conductive thread) to two electrical terminals (e.g., bus bars) near opposite edges of the heating element 34. Such embodiments may maintain flexibility and durability of the heating element 34 with repeated flexing. The electrical terminals may supply current to the heating element 34. Resistance across the heating element 34 may generate heat. The resistance of the heating element 34 is typically directly related to heat generation according to the following relationship: Q=I² R where Q is the heat generated in units of Joules, I is the current flow through the heating element 34 in units of Amperes and R is the resistance of the heating element 34 in units of Ohms.

As seen in FIGS. 2 and 4, the heated layer 30 can be coupled to an adjacent surface of the base layer 20. The heated layer 30 may be coupled to the base layer 20 in a way that maintains the alignment of the heated layer 30 as it rests on the base layer 20 yet allows maximal independent flexion between the base and heated layers 20, 30. The heated layer 30 and the base layer 20 can be coupled using any means known in the art. Some exemplary means of coupling the heated layer 30 and the base layer 20 include heat, radio frequency (RF) or ultrasound welding techniques, bonding via a solvent or an adhesive, sowing with thread and/or riveting. When coupled, the heated layer 30 and the adjacent surface may form an attached area (e.g., areas 36, 38 seen in FIGS. 5-7). In some embodiments, the attached area is less than an area of contact between the heated layer 30 and the adjacent base layer 20, allowing at least a portion of the heated layer 30 to be folded substantially independently of the base layer 20 as shown in FIGS. 8A-D. The attached area can be across at least a portion of an end (e.g., near foot end) of the mattress 10 as seen in FIGS. 5 and 6. In other words, the when coupled along the periphery of the base layer 20 and heated layer 30, they form an attached area 36 across at least a portion of an end of the mattress 10. Alternatively, the attached area 38 of the heated layer 30 and the base layer 20 may extend along a midline of the mattress 10 in a central region as shown in FIG. 7. These examples are not meant to limit other areas of attachment between the two layers. The heated layer 30 may not be bonded to the base layer 20 across the entire opposing surfaces or around the entire peripheries. The base and heated layers 20, 30 may be free to fold and bend substantially independently of one another. The attached area (e.g., areas 36, 38) of the heated layer 30 and the base layer 20 may include one or more detachable means, including but not limited to buttons, straps, snap closures, and/or hook and loop fasteners (e.g., button 28 and strap 26 shown in FIG. 1) which may attach the base layer 20 to the heated layer 30. Such a coupling between the two base and heated layers 20, 30 may be secure enough to assure that the heated layer 30 cannot slide independently of the base layer 20.

The electrical heating element 34 may have elastic properties (e.g., be stretchable). The electrical heating element 34 can be coupled to the heated layer 30 around at least a portion of its periphery. The electrical heating element 34 may include a fabric coated with an electrically semi-conductive material. In some embodiments, the conductive or semi-conductive coating may be a polymer and the bonding process is polymerization. The coating on each individual thread of polymer may allow maximal flexibility and may not crack, fracture or delaminate during flexion. Polymerization of these conductive or semi-conductive materials on individual fibers of the carrier fabric can be an optimal process for producing a durable, flexible and stretchable heater. In some embodiments, the electrically semi-conductive material is polypyrrole. Alternatively, the electrical heating element 34 includes one or more of conductive fabrics and films. The conductive fabrics can be at least one of carbon fiber, carbonized fibers, woven substrates coated with semi-conductive or conductive coating, non-woven substrates coated with conductive or semi-conductive coating, carbonized ink, metalized ink and/or carbon impregnated plastic films. However, other coatings are also anticipated and conductive coatings that use carbon or metal as the conductive material are also anticipated. Such coatings may provide an electrically semi-conductive fabric heater that may be highly flexible, durable, may have elastic properties and may not fracture either the carrier fiber or the semi-conductive polymer coating with repeated flexing, loading and stretching. Additionally, the heater fabric may not require lamination for mechanical stabilization.

The electrical heating element 34 which may be a coated fabric may be further coated with a thin layer of elastomeric material such as silicone rubber. Other elastomers are also anticipated. Elastomers may offer a liquid-proof coating and prevent liquid ingressing into the fabric. The purpose of coating one or both sides of the heater element with an elastomer may be to protect the heater fabric from damage by liquids and oxidation. The coating of silicone rubber may also provide electrical insulation in the event that adjacent areas of heater surface contact one another, shorting the electrical pathway. Very thin layers of silicone rubber (e.g., thinner than the fabric of the heating element) will suffice and add minimal stiffness to the construction. Alternately, thermoplastic elastomers or plastic films may be applied to one or both sides of the heater material.

According to some exemplary embodiments, the conductive fabric of the electrical heating element 34 may include a woven polyester sheet being coated with polypyrrole. The coated fabric may have an average electrical resistance, of approximately 15-30 ohms per square at about 48 volts, as determined with an exemplary four point probe resistance measurement method. Such fabrics may provide a desirable heat generation which may be quantified by the fabric's watt density, or, the rate of heat generated per unit surface area of the fabric. In some embodiments, the heating element 34 may provide a substantially uniform watt density output across the surface of the fabric. For instance, the watt density output of the heating element 34 can be less than approximately 0.5 watts/sq. inch. Alternatively, the watt density output of the heating element 34 can be between approximately 0.2 and approximately 0.4 watts/sq. inch, across a surface area. The surface area may include and extend between lateral edges of the heating element 34. The electrical resistance of the conductive fabric may be suitable to produce a watt density of between approximately 0.2 watts/sq. in and approximately 0.4 watts/sq. in. when a width of the fabric is approximately 16-28 inches. Such a width may be suitable for a mattress 10 heating assembly, some embodiments of which will be described below.

In some exemplary embodiments, the electrical heating element 34 may have variable electrical resistance. As the electrical resistance is related to the heat generated by the fabric as described previously, variability in resistance thus translates to variability in heat generated by the heating element 34. For instance, the electrical resistance of the heating element 34 (e.g., a conductive fabric) may be tailored based on the geometry of the electrical heating element 34 (e.g., width of the fabric between electrical connections). An exemplary embodiment may have the width of the conductive fabric of the electrical heating element 34 varying inversely with electrical resistance. Other examples may include varying the electrical resistance by increasing or decreasing a surface area of the fabric that can receive the conductive coating, or, by increasing or decreasing the basis weight of the fabric. Alternatively, or in addition, the resistance of such conductive fabrics may vary over surface areas, for example, due to variation in a thickness of a conductive coating, variation within the conductive coating itself, variation in effective surface area of the substrate which is available to receive the conductive coating, or variation in the density of the substrate itself. In such embodiments, precise temperature control may be provided, particularly if the mattress 10 is used for patient warming during surgery.

Referring back to FIG. 4, the mattress 10 may include a control temperature sensor 40 coupled to the electrical heating element 34. The control temperature sensor 40 can be positioned substantially in line with a longitudinal midline of the electrical heating element 34, along which direction a patient may lay. Such embodiments may provide a safe and effective temperature control and may facilitate contact between the control temperature sensor 40 and the patient. The control temperature sensor 40 may regulate the heat supplied to the patient during surgery and ensure that the patient does not receive burn injuries due to excess heat supplied accidentally due to variable resistance of the heating element 34.

With continued reference to FIG. 4, the contact between the control temperature sensor 40 and the patient may be adjusted to fit the patient size and position on the mattress. Typically, control temperature sensor 40 contact with an adult patient can be accomplished more easily because an adult patient may cover most of the surface of the mattress 10 (on a narrow operating table). However, pediatric patients may not be aligned and/or suitably positioned on the mattress 10 and may inadvertently fail to contact the control temperature sensor 40. To assure accurate patient positioning relative to the control temperature sensor 40, various embodiments may include two or more substantially elongated positioning members. For instance, as illustrated in FIGS. 2 and 3, the base layer 20 may include at least two elongated positioning members 42 aligned substantially parallel and lateral to the longitudinal midline of the mattress 10 and projecting upward from the base layer 20. Alternatively, the base layer 20 includes at least two elongated inflatable tubes aligned substantially parallel and lateral to the longitudinal midline of the mattress and projecting upward from the base layer 20 when inflated. The elongated positioning members 42 may protrude upward between 0.75 and 2.5 inches from the upper surface of the base layer 20. The elongated positioning members 42 may be made of foam. The elongated positioning members 42 may be triangular in cross-section, approximately 4-12 inches long and positioned approximately 5 to 8 inches apart (2.5-4 inches from the midline) in the region of the mattress 10 the corresponds to the location of the patient's torso and legs.

As seen in FIGS. 8A-8D, the elongated positioning members 42 may project upward into the heated layer 30, causing the heated layer 30 to form a trough 44 between the positioning members 42. The midline trough 44 may accommodate a pediatric patient's body and center it on the midline as shown in FIG. 8A. If the pediatric patient is not centered in the midline of the trough 44, the positioning members 42 may cause the pediatric patient to be contorted, thereby alerting the surgical staff that repositioning may need to be performed to correct the alignment/positioning of the patient. The control temperature sensor 40 may be attached to the heating element 34 in the heated layer 30, in a central location that corresponds substantially to the center of the trough 44. Therefore, the positioning trough 44 created by the elongated positioning members 42 in the base layer 20 may facilitate positioning the pediatric patient in contact with the control temperature sensor 40.

Referring back to FIG. 4, the electrical heating element 34 may be sandwiched between a first sheet 46 of a shell and a second sheet 48 of the shell. The first and second sheets 46, 48 may be bonded together around their peripheries (e.g., at peripheries 50) to form a substantially liquid-proof enclosure. The shell may protect and isolate the heating element 34 from an external environment of the mattress 10 and may further protect a patient disposed on the mattress 10 from conditions such as potential electrical shocks. According to some preferred embodiments of the present invention, the shell is liquid-proof to prevent fluids, (e.g., bodily fluids, IV fluids, or cleaning fluids, and the like) from contacting the heater assembly, and may further include an anti-microbial element, such as silver ions coated on the fabric (e.g., SILVERion™ antimicrobial fabric). Further, bonding around the periphery of the mattress 10 may create a shell without folds, creases, crevasses or sewing needle holes that could collect infectious debris and could be difficult to clean. In some embodiments, a layer of plastic film may (not shown) be placed over each broad surface of the heating element 34, but may not be bonded thereto.

The conductive fabric of the heating element 34 can be anchored around its periphery to the shell and thus held in an extended and wrinkle-free condition. In this embodiment, strips of plastic film may be coupled to the edges of the fabric by sewing. The strips may extend laterally and may also extend longitudinally beyond the ends of the fabric. The strips of plastic film may be made of the same material as the shell and therefore can be bonded around the periphery of the mattress 10, into the bond between the first sheet of the shell and second sheet of shell.

With continued reference to FIG. 4, in exemplary embodiments, the heated layer 30 may include a layer of high-loft fibrous thermal insulation 52 proximate the electrical heating element 34. The thermal insulation 52 may be located on the underside of the heating element 34, away from the patient contact surface. In some embodiments, the thermal insulation layer 52 can be fibers of polyethylene terephthalate or a mixture of polyethylene terephthalate and polypropylene (e.g., Thinsulate™).

In some embodiments, the layer(s) of foam 24 of the base layer 20 and the heating element 34 may both be covered by one or more sheets 54, 56 of a shell. While any polymer of appropriate thickness such as 10-30 mils can be suitable for use with the shell, some exemplary polymers include polyurethane and/or PVC. Such polymers retain strength and flexibility during routine use. Other polymers (e.g. Naugahyde) such as a polymeric film extruded onto a woven fabric may also be used. The sheets can be bonded to each other and/or to the heating element 34 by any means known in the art. Some exemplary means include by heat, radio frequency (RF), ultrasound welding, bonding via a solvent and/or an adhesive or by sewing with thread. For instance, the first and second sheets 46, 48 can be bonded together at periphery 50 to form a substantially liquid-proof enclosure (e.g., a hermetically-sealed pouch) in which the electrical heating element 34 can be sandwiched. Likewise, a third sheet 54 of the shell and a fourth sheet 56 of the shell may be bonded together around their peripheries 60 to form a substantially liquid-proof enclosure (e.g., a hermetically-sealed pouch) around base layer 20. One or more layers of foam forming the base layer 20 may be sandwiched between the third and fourth sheets 54, 56 of the shell. This arrangement may prevent any damage to the heated and base layers 30, 20 due to liquids (e.g., bodily fluids released by a patient during surgery).

Embodiments of the invention also include a method of positioning a patient on the mattress. The method may involve the step of providing a mattress according to certain embodiments disclosed herein. The base layer of the mattress may be connected to the operating table. Any known connection means between the base layer and the operating table are contemplated. The patient may be positioned on top of the heated layer, substantially in a central region or on the midline of the mattress. Reference is now made to FIGS. 8A-8D. As seen in FIG. 8A, a patient 62 is positioned substantially on the midline trough 44 of the mattress 10. After the patient 62 is positioned substantially in the midline of the mattress, the lateral sides 64 of the heater layer 30 that extend beyond the sides 66 of the patient may be folded upward as shown in FIG. 8B so that they closely approximate or contact the sides 66 of the patient 62. This folding of the heated layer's sides 64 upward along the side 66 of the patient 62 may be performed by the surgical staff. As seen in FIG. 8C, the heated layer 30 may be held in the folded position by inserting positioning rolls 68 (e.g., rolled towels, sheets and the like) or high-loft fibrous material or polymeric foam between the base layer 20 and the underside of the heated layer 30. Two or more positioning rolls (e.g., as seen in FIG. 8D) may be placed under the heated layer 30. Alternatively, the base layer 20 may include two or more elongated longitudinal air bladders (not shown) near the side edges. The air bladders can be inflated to elevate the sides of the heated layer to a position proximate the side of the patient, thereby holding the heated layer to the sides 66 of the patient 62 during surgery.

In some embodiments, patient-positioning rolls may be placed under the heated layer to maintain maximal heat transfer characteristics while allowing complex patient positioning. For example, small rolls of towels are frequently placed under the chest/shoulder blades of pediatric patients in order to put their back into extension and improve access to their upper abdomen. If this positioning roll is placed above the standard heated mattress, the roll lifts half of the patient's body off of the heated surface. Naturally this may reduce the heat transfer between the mattress and the patient. In contrast, various embodiments allow the positioning roll to be placed under the heated layer and the heating element may thus stay in conductive thermal contact with an entire anterior or posterior surface of the patient.

Such embodiments may offer one or more benefits. By substantially separating the heating function from the support function, various embodiments may allow the heated layer to maximally contact the non-weight-bearing side surfaces of the patient for enhanced heat transfer, especially for the pediatric patients. Certain embodiments may allow the body surface area in contact with the heated surface to approximately double in comparison to known heated mattresses. Various embodiments may significantly increase the heat transfer effectiveness of the mattress, especially in pediatric patients, while maintaining improved safety with regards to patient positioning, folding or bunching of the heater under the patient. By separating the heater layer from the base layer, the better support and enhanced heat transfer may both be accomplished during surgery.

Thus, embodiments of the invention are disclosed. Although the present invention has been described in considerable detail with reference to certain disclosed embodiments, the disclosed embodiments are presented for purposes of illustration and not limitation and other embodiments of the invention are possible. One skilled in the art will appreciate that various changes, adaptations, and modifications may be made without departing from the spirit of the invention. 

What is claimed is:
 1. A method of positioning a patient on a conformable heated mattress for therapeutic under-body warming during surgery, comprising: positioning a conformable heated mattress on an operating table, the mattress comprising: a heated layer comprising: a flexible, sheet-like electrical heating element, a shell comprising a first sheet and a second sheet bonded together around their peripheries to form a substantially liquid-proof enclosure, wherein the electrical heating element is sandwiched between the first and second sheets, and a base layer having a surface adjacent to and beneath the second sheet of the shell, wherein the second sheet of the shell is coupled to the surface of the base layer forming an attached area wherein the attached area is less than an area of the second sheet allowing at least a portion of the heated layer to be folded substantially independently of the base layer; positioning the patient on top of the heated layer; folding one or more portions of the heated layer upwards along the lateral sides of the patient; and placing at least one positioning element between the heated layer and the base layer to hold the heated layer proximate the sides of the patient.
 2. A mattress for therapeutic under-body warming during surgery, the mattress comprising: a heated layer comprising; a flexible, sheet-like electrical heating element, a shell comprising a first sheet and a second sheet bonded together around their peripheries to form a substantially liquid-proof enclosure, wherein the electrical heating element is sandwiched between the first and second sheets; and a base layer beneath the heated layer and having a surface adjacent to the heated layer, wherein the heated layer is coupled to the surface of the base layer forming an attached area, wherein the attached area is less than an area of the heated layer contacting the base layer.
 3. The mattress of claim 2 wherein the heated layer includes a layer of high-loft fibrous thermal insulation proximate the electrical heating element.
 4. The mattress of claim 2 wherein the electrical heating element is coupled to the heated layer around at least a portion of its periphery.
 5. The mattress of claim 2 wherein the electrical heating element includes one or more of conductive fabrics and films comprising at least one of carbon fiber, carbonized fibers, woven substrates coated with semi-conductive or conductive coating, non-woven substrates coated with conductive or semi-conductive coating, carbonized ink, metalized ink and carbon impregnated plastic films.
 6. The mattress of claim 5, wherein the electrically semi-conductive material is polypyrrole.
 7. The mattress of claim 2, further comprising a control temperature sensor coupled to the electrical heating element, the control temperature sensor positioned substantially in line with a longitudinal midline of the electrical heating element.
 8. The mattress of claim 2, wherein the first sheet of the shell includes a polymeric film
 9. The mattress of claim 8, wherein the polymeric film is one of polyurethane and PVC.
 10. The mattress of claim 8, wherein the polymeric film is extruded onto a woven fabric.
 11. The mattress of claim 2, wherein the first sheet of the shell and the second sheet of the shell are bonded by one of heat welding, radio frequency welding, ultrasound welding, solvent bonding, adhesive bonding and sewing.
 12. The mattress of claim 2, wherein the base layer comprises a third sheet of the shell and a fourth sheet of the shell that are bonded together around their peripheries to form the substantially liquid-proof enclosure.
 13. The mattress of claim 12, wherein the base layer comprises a layer of foam sandwiched between the third and fourth sheets of the shell.
 14. The mattress of claim 15, wherein the third and fourth sheets of the shell is bonded by one of heat welding, radio frequency welding, ultrasound welding, solvent bonding, adhesive bonding and sewing.
 15. The mattress of claim 2, wherein the heated layer and the base layer are bonded by one of heat welding, radio frequency welding, ultrasound welding, solvent bonding, adhesive bonding, sewing and riveting.
 16. The mattress of claim 2, wherein the attached area of the heated layer and the base layer includes one or more detachable means, the one or more detachable means comprising buttons, straps, snap closures and hook and loop fasteners.
 17. The mattress of claim 2, wherein the attached area of the heated layer and the base layer is across at least a portion of an end of the mattress.
 18. The mattress of claim 2, the attached area of the heated layer and the base layer is substantially along at least a portion of a midline of the mattress.
 19. The mattress of claim 18, wherein the base layer includes at least two elongated positioning members aligned substantially parallel and lateral to the midline of the mattress and projecting upward from the base layer.
 20. The mattress of claim 18, wherein the base layer includes at least two elongated inflatable tubes aligned substantially parallel and lateral to the midline of the mattress and projecting upward from the base layer when inflated. 